The Institute of Cetacean Research reached an agreement last year with Sea Shepherd US, but it was unclear whether that covered Sea Shepherd Australia.

The institute said it did not wish to comment on the latest events in the Southern Ocean, but said its research programme conformed to a 2014 International Court of Justice decision and the International Convention for the Regulation of Whaling.

It confirmed it was targeting 333 black minke whales, but said the work involved what it called a "non-fatal investigation".